The present invention relates to an exhaust gas recirculation system in a motor vehicle comprising a differential pressure measuring unit. In particular, the invention relates to a method for checking a functionality of a differential pressure measuring unit provided in such an exhaust gas recirculation system.
Exhaust gas recirculation systems are used in motor vehicles, inter alia, in order to reduce pollutant emissions in exhaust gases from an internal combustion engine. To this end, exhaust gases originating from the internal combustion engine are directed, at least in part, back into the internal combustion engine. By feeding such exhaust gases, in addition to fresh air, which is also fed, to the internal combustion engine, it is possible to reduce a formation of nitrogen oxides, for example, during combustion, given that the exhaust gases, as inert gas, are chemically inactive.
In order to optimize the combustion in the internal combustion engine, a rate at which exhaust gases are recirculated should be matched as exactly as possible to an impending operating state of the internal combustion engine. In order to enable an exhaust gas recirculation rate to be influenced, an exhaust gas return flow valve is disposed, for this purpose, in an exhaust gas recirculation channel, through which exhaust gases from the internal combustion engine are directed back into an air intake channel, which exhaust gas return flow valve is designed to be capable of controllably throttling an exhaust gas flow in the exhaust gas recirculation channel.
In order to enable a desired exhaust gas recirculation rate to be set as precisely as possible with the aid of the exhaust gas return flow valve, it should be possible to precisely determine the exhaust gas recirculation rate actually prevailing during the operation of the internal combustion engine. To this end, it can be provided, for example, to measure an opening cross section of the exhaust gas return flow valve, a differential pressure across the exhaust gas return flow valve, and an exhaust gas temperature and, on the basis thereof, to determine the exhaust gas recirculation rate.
A method for determining a low-pressure exhaust gas recirculation mass flow in an air system of an internal combustion engine is described, for example, in DE 10 2011 017 779 A1.
In conventional exhaust gas recirculation systems, however, a functionality of a differential pressure measuring unit, which is used for measuring the differential pressure across the exhaust gas return flow valve, generally cannot be checked. In particular, it cannot be checked whether one or multiple pressure sensors, which are supposed to measure a currently prevailing pressure in the exhaust gas to be recirculated, upstream of the exhaust gas return flow valve on the one hand and downstream of the exhaust gas return flow valve on the other hand, so that, on the basis thereof, the differential pressure can be determined, function correctly, and/or corresponding connections to the exhaust gas recirculation channel are intact.